Bernstein wrote for The New Yorker magazine. During World War II, he was a war correspondent for the U.S. Army newspaper Yank and because of his Communist affiliations was given the chance to interview Josip Tito the leader of the Yugoslav Communist Partisans in 1944. Bernstein Walter Bernstein is cited in an October 1944 KGB report as welcoming "the re-establishment of liaison" with Soviet intelligence.
In 1951, because of his Communist ties, Bernstein was called to testify before the House Un-American Activities Committee (HUAC). His uncooperative performance before the committee did little to stay the fears of the Hollywood producers and he was blacklisted along with several others.
He also wrote for the 1953 television segments, You Are There, featuring Walter Cronkite.
In 1977 Bernstein made a cameo appearance as an actor in Woody Allen's film Annie Hall.
In 1996, Bernstein published a book about the blacklisting period titled Inside Out: A Memoir of the Blacklist. In his memoirs Bernstein stated while at Dartmouth College he first joined the Young Communist League in 1937.
Bernstein is referenced in the NSA Archives of the Venona project transcripts 23 October 1944. The transcript discusses the re-establishment of liaison between KhAN and Walter Sol Bernstein. "Khan" remained unidentified by NSA and FBI counterintelligence analysts, but is thought to be Avram Landy, a senior Communist Party official.
Bernstein is referenced in the following Venona project transcripts:
- 1509 KGB New York to Moscow, 23 October 1944, p.1
- 1509 KGB New York to Moscow, 23 October 1944, p.2
- 1509 KGB New York to Moscow, 23 October 1944, p.3
- National Security Agency Archives (23 October 1944)
- Walter Bernstein, Inside Out: A Memoir of the Blacklist (New York: Knopf, 1996), 124, 228.
- Harvey Klehr, John Earl Haynes, Venona: Decoding Soviet Espionage in America (New Haven: Yale University Press, 1999), pgs. 238–240. ISBN 0300077718
- Harvey Klehr, John Earl Haynes, and Fridrikh Igorevich Firsov, The Secret World of American Communism (New Haven: Yale University Press, 1995). ISBN 0300068557
- Harvey Klehr, John Earl Haynes, and Kyrill Anderson, The Soviet World of American Communism (New Haven: Yale University Press, 1998). ISBN 0300071507
- A Counterintelligence Reader, Vol. 2, Chap. 4, National Counterintelligence Center (NACIC).
- Allen Weinstein, The Haunted Wood: Soviet Espionage in America—the Stalin Era coauthored with Alexander Vassiliev, (New York: Random House, 1999).